The invention relates to a multiple drive for a heavy load application, i.e. a multiple drive for a vertical mill for cement production or similar, for example, and to method for operating such a multiple drive.
DE 10 2011 079 555 A1 discloses a drive arrangement for a vertical roller mill comprising a plurality of electric motors over which the total drive load is evenly distributed during operation. EP 1 770 852 A discloses a method for starting up a production machine, wherein startup is effected by means of a hydraulic motor and continuous operation takes place by means of an electric motor. EP 0 680 136 A discloses a method for soft-starting the drive motors of a rotor spinning machine. These each independently drive individual operating elements of the machine, e.g. a main suction system, a tailstock rotor, a headstock rotor, and opening rollers. Under the control of a soft-start controller, the drive motors are supplied with a base voltage during a predefined run-up time and thereafter with a line voltage, and the soft-start controller specifies the run-up sequences of the individual motors.
In the case of drives for vertical mills without frequency converters, starting aids are used for the startup process. Starting aids are to be understood here as meaning, for example, liquid starters, soft starters and also fluid couplings. The purpose of such starting aids is to adjust the starting torque produced, and the starting current occurring, to a desirable level. The startup process places a particular load on the drive, resulting, among other things, in excessive heating of drive components such as a starter or fluid coupling. An undesirable cooling time is often inevitable if several startup attempts are required or the drive components in question are heated for other reasons.